1. Take a new server and install Windows NT from scratch as a BDC of the current network 2. After installation is finished and all the windows updates are installed, promote this machine to PDC. 3. Disconnect this machine from the network and upgrade to Windows 2000. 4. Update machine with service packs and other updates. 5. Check that no problems exist. Connect this server to an isolated hub and connect one of the machines that are connected to the NT BDC to this hub and make sure there is no problem login to the domain. 6. If no problems are found, move everything together and now upgrade the BDC (the original network PDC) an upgrade to 2000.